A New Method to Improve Soap Separation in Black Liquor by Adding Extracted Neutrals of Tall Oil, 2004 Engineering, Pulping, and PCE&I Conference

The separation of soap from black liquor is restricted in black liquor particularly in the conditions of brown stock washing.

The dynamics of phase separation in solutions of model soaps was investigated by light transmission and backscattering measurements using the TurbiScan MA2000 (TSMA) and TurbiScan (TS) Online analyzers. The results showed that the separation (creaming) rate of soap is highly dependent on the ratio of fatty and resin acid soaps and the content of neutrals. A narrow two-phase region was found in which the fatty + resin acid soaps and neutrals form lamellar liquid crystals of soap and neutrals were in equilibrium with a dilute solution.

The resulting effect decreases the share of soluble soap and increases the share of insoluble soap. The findings lead to a patent pending method for reducing the solubility of soaps in black liquor by adding isolated tall oil soap neutrals into black liquor. In the mill trial, the effect of the neutrals addition was monitored by measuring the concentration of the soluble and total amount of soap in the washing filtrate system. It was observed that the amounts of soluble fatty acid and resin acid soaps were remarkably reduced, even 70-80 %, depending on the amount of the auxiliary neutral substances added.